1. Field of the Invention
This invention relates generally to the field of computer systems and more specifically to optimizing flow of information between components in computer systems.
2. Description of the Related Art
Prior art systems often use a configuration of components as illustrated in FIG. 1. CPU 101 (a Central Processor or Processor) is coupled through a Processor Bus 102 to a component referred to as a Host Bridge 105, and thereby coupled to the rest of the system. Host Bridge 105 is coupled to Memory 103, the main memory of the system, and Host Bridge 105 is also coupled to I/O Bridge 107 (Input/Output Bridge). I/O Bridge 107 couples to Keyboard 109, Mouse 111, and Disk Drive 110, and may couple to other components in a bus or point-to-point fashion. Through these couplings, CPU 101 is coupled to each component in the system, and may read or write information to each of the devices (within the capabilities of those devices).
Further extending the complexity of the system, PCI Bus 125 (Peripheral Component Interconnect Bus based on the Peripheral Component Interconnect Bus Specification Revision 2.1 or 2.2 from the Portland PCI Working Group as published by Intel Corporation) may be involved in the coupling of Host Bridge 105 to I/O Bridge 107, and may thereby couple PCI Agents 120, other devices on the PCI Bus 125. Thus, through Host Bridge 105, CPU 101 may communicate with PCI Agents 120. While it is advantageous to make PCI Agents 120 available to the system, incorporating the PCI Bus 125 into a coupling or connection between two components further complicates the physical devices and layout, and the protocols for communication over that coupling.
A method and apparatus for reducing flow control and minimizing interface acquisition latency in a hub interface is a method of transferring data between a control hub coupled to a hub interface which is coupled to an input-output hub including the following: Transferring the data in packets. Prioritizing isochronous transfers over asynchronous transfers. Limiting asynchronous transfers to 32 bytes per packet when an agent requests the hub interface, and limiting asynchronous transfers to 64 bytes per packet when no requests for the hub interface are recognized.